Mechanism of metallization and superconductivity suppression in YBa₂(Cu_0.97Zn_0.03)₃O_6.92revealed by⁶⁷Zn NQR

Abstract

We measure the nuclear quadrupole resonance signal on the Zn site in nearly optimally doped YBa 2 Cu 3 O 6.92 , when Cu is substituted by 3% of isotopically pure 67 Zn. We observe that Zn creates large insulating islands, confirming two earlier conjectures: that doping provokes an orbital transition in the CuO 2 plane, which is locally reversed by Zn substitution, and that the islands are antiferromagnetic. Also, we find that the Zn impurity locally induces a breaking of the D 4 symmetry. Cluster and DFT calculations show that the D 4 symmetry breaking is due to the same partial lifting of degeneracy of the nearest-neighbor oxygen sites as in the LTT transition in La x 2− Ba x CuO 4 , similarly well-known to strongly suppress superconductivity (SC). These results show that in-plane oxygen 2p 5 orbital configurations are principally involved in the metallicity and SC of all high-T c cuprates, and provide a qualitative symmetry-based constraint on the SC mechanism.

Emergence of superconductivity in the cuprates via a universal percolation process

“…3b, the doping dependencies of the two characteristic fields are remarkably similar, including a minimum close to the “1/8 anomaly” of LSCO and YBCO 8,44,45 . The substitution of 3% Cu with Zn in YBCO causes a dramatic decrease of H 0 , in agreement with established effects of Zn on superconductivity in cuprates 36 .…”

“…Measurements of the in-plane linear and nonlinear response were performed for three representative cuprate families: a nearly optimally doped sample of HgBa 2 CuO 4+ δ (Hg1201), a model cuprate system due to its simple structure, high T c , and minimal point disorder effects 32–35 ; an optimally doped YBa 2 Cu 3 O 7− δ (YBCO) sample with 3% of Cu substituted by Zn (YBCO–Zn), where Zn dramatically affects the superconducting properties 36 ; and La 2− x Sr x CuO 4 (LSCO), spanning a wide range of doping across the superconducting dome (see Table 1). For all samples, σ 3 exhibits qualitatively the same temperature dependence (Fig.…”

“…32,36 , respectively. As described in the text, T c corresponds to the peak in the nonlinear conductivity; we estimate the error to be less than 1%.…”

“…YBCO–Zn is an oriented powder sample with 3% Cu substituted with Zn, which enables us to discern effects of intentionally introduced CuO 2 plane disorder. This sample was prepared using a standard solid-state reaction, used in prior Zn nuclear quadrupole resonance experiments and characterized in detail 36 . See Table 1 for additional sample information.…”

Synthesis of murunskite single crystals: A bridge between cuprates and pnictides

“…While superconductivity is observed in both material families, it involves the oxygen ligands in the cuprates, but not the arsenic ligands in the pnictides [8]. Elucidating the connection between the macroscopic functional properties and the microscopic orbitals responsible for them is a major contemporary research frontier at the interface of physics and chemistry [9][10][11][12][13][14].…”